Exemplary embodiments of the present invention relate to a complex supercritical CO2 generation system, and more particularly, to a complex supercritical CO2 generation system capable of increasing heat exchange efficiency to improve a system output.
Internationally, as a necessity for efficient generation is increasing more and more and a movement to reduce pollutant emissions is becoming more and more active, various efforts to increase power production while reducing the pollutant emissions have been conducted. As part of the efforts, research and development into a power generation system using supercritical CO2 as a working fluid has been actively conducted.
The supercritical CO2 has a density similar to a liquid state and viscosity similar to gas, such that equipment may be miniaturized and power consumption required to compress and circulate the fluid may be minimized. At the same time, the supercritical CO2 having critical points of 31.4° C. and 72.8 atm is much lower than water having critical points of 373.95° C. and 271.7 atm, and thus may be handled very easily. The supercritical CO2 generation system shows pure generation efficiency of about 45% when being operated at 550° C. and may improve generation efficiency by 20% or more as compared to that of the existing steam cycle and reduce the size of a turbo device. One example of the supercritical CO2 generation systems is a parallel recuperation type supercritical CO2 generation system disclosed in Korean Patent Application No. 2016-0157112.
FIG. 1 is a schematic diagram showing a cycle of the parallel recuperation type supercritical CO2 generation system. As shown in FIG. 1, the system includes a first separator S1 disposed at a rear end of the compressor 100, in which a working fluid is compressed by the compressor 100 and then branched to a direction 7 of a low temperature heater 330 and a direction 10 of a recuperator unit 200 from the first separator S1. The working fluid branched to the recuperator unit 200 is again branched to a direction 13 of the first recuperator 210 and a direction 11 of a second recuperator 230, respectively, via a second separator S2. The working fluid passing through a first turbine 410 and a second turbine 430 passes through only one of the first recuperator 210 and the second recuperator 230, respectively, and is cooled and then transmitted to the compressor 100.
However, in the existing generation system, since an outlet temperature of the compressor is a value determined in consideration of the efficiency of the compressor, a pressure drop of the recuperator, or the like, the outlet temperature cannot be increased beyond a certain level, which limits an increase in an output of the cycle. Further, since an inlet temperature of the second turbine follows a value slightly lower than an outlet temperature of the first turbine, the higher the highest temperature of the turbine inlet, which is the inlet temperature of the first turbine, the higher the inlet temperature of the second turbine. However, since there is a heat transfer limit in a high temperature heater or a low temperature heater under high temperature conditions of an external heat source (phenomenon that temperature of feed lines 8 and 9 through which the working fluid goes to the high temperature heater 310 via the low temperature heater 330 approaches temperature of B), there is a limit in increasing an output by increasing the inlet temperature of the first turbine.